If they don't change something with imbuing you can have -20 mage weapon as lowest value...
Ingredienta needed are:
SC Magical residue, diamomd and 10 silver snake skin
FC 1 (with SC you get the -1 FC) relic fragments, ruby and 10 essence of achievement
DCI 15 relic fragments, tourmaline and 10 essence of singularity
-20 mage weapon enchanted essence, emerald and 10 arcanic rube stones
These are the ingredients for only 1 weapon